Sinonasal-inverted papilloma is a benign tumour with a high rate of recurrence, but possible malignant transformation. Therefore, inves tigation of predisposition to malignant transformation of sinonasal-inverted papilloma gives clinicians the opportunity for adequate trea ment. Topoisomerase II-α (topoII-α) and Ki67 are markers of cell proliferation in both normal and neoplastic tissues and its level o expression could be used as a predictive parameter. Our goal was to investigate by immunochemistry the expression level of topoII-in inverted papilloma, inflammatory nasal polyp and normal sinonasal epithelium and to compare it with expression level of Ki67. TopoI α nuclear immunostaining showed a differential positivity in the investigated cases. The topoII-α index was 30.6 ± 12.8 in inverte papilloma, 10.7 ± 6.6 in the adjacent epithelium of inverted papilloma, but only 2.3 ± 2.0 in the normal sinonasal epithelium. The di ferences in topoII-α expression between inverted papilloma and normal sinonasal epithelia were statistically significant. In inflammator nasal polyp group, topoII-α index was 2.4 ± 2.1, and the difference in the topoII-α index between inverted papilloma and inflammator polyp group was also statistically significant. Nuclear immunostaining for Ki67 followed a similar variation. The Ki67 index was 50.0 ± 20. in inverted papilloma, 9.0 ± 6.6 in the adjacent epithelium of inverted papilloma and 2.4 ± 0.9 in normal sinonasal epithelium. The di ferences in Ki67 expression between inverted papilloma and either adjacent or normal sinonasal epithelia were statistically significan Significant correlation coefficients were found between topoII-α and epithelial thickness (r = 0.70, P > 0.0001), and between Ki67 inde and epithelial thickness (r = 0.71, P> 0.0001). In the inflammatory nasal polyp group Ki67 index was 5.9 ± 3.4. The difference in th Ki67 index between inverted papilloma and inflammatory nasal polyp groups was statistically significant. Significant correlation coeff cient was found between topoII-α index and Ki67 index in inverted papilloma (r = 0.42, P > 0.05). These results suggest that the inverte papilloma contains a significantly higher cell population with proliferative activity by comparison with normal sinonasal and inflamma tory polyp epithelia, showing a significant correlation between topoII-α and Ki67 expression, and indicating that topoII-α could be a independent prognostic factor for a putative malignant transformation.